For improving image quality in ink-jet printing, primer compositions have been used to improve the interaction between the recording medium and the inks.
Primer compositions normally contain salt compositions with acidic and/or electrophilic properties in order to destabilize pigment color particles. As a result, the behaviour of the pigment particles upon drying of the printed medium is optimized. Uncontrollable ink drop coalescence (‘puddling’) and color bleed is prevented, and the optical color density improved.
U.S. Pat. No. 5,985,424 discloses an inkjet recording sheet comprising a cellulosic sheet support, e.g., paper, having on at least one surface thereof an inkjet coating comprising, in combination, a porous base coat having a high absorption capacity for absorbing the vehicle of an inkjet ink, and an ink receiving coat having a superior capacity for keeping the dyes in the ink on the surface with minimal spreading, tailing or blurring, to provide a sharp image.
US2008/0092309 pertains to inkjet printing on fabric and to a pretreatment solution for the fabric that allows high quality printing thereon. The aqueous pretreatment solution/emulsion comprises a nonionic latex polymer and a multivalent cationic salt.
In US2007/0054981, an ink set comprising an ink containing at least an organic pigment, a water-soluble organic solvent and water and a treating liquid which is applied to a recording medium before applying the ink to the recording medium and produces an agglomerate upon contact with the ink, the ink containing a low molecular weight dispersant having a molecular weight of 2000 or lower and polymer fine particles is described.
US 2006/0293410 discloses an ink set for an inkjet comprising an ink and a processing liquid, wherein at least one of the ink and the processing liquid contains a water-soluble non-linear polymer. The non-linear polymer has at least one selected from the group consisting of a branched structure, a cross linking structure and a mesh structure in a molecule.
Further, US 2005/0225616 describes an ink-jet printing process comprising the steps (a) and (b) in any order or simultaneously: (a) applying an ink to a substrate by means of an ink-jet printer to form an image on a substrate; and (b) applying to the substrate a fixing composition comprising a liquid medium and a polymer containing a plurality of monoguanide and/or biguanide groups by means of an ink jet printer; characterised in that in the fixing composition has a chloride concentration less than 400 ppm by weight.
In addition, ink sets and related methods are provided in US 2014/0362137. An ink set can comprise an ink including an ink colorant and an ink vehicle, the ink devoid of metal salt; a treatment fluid including a latex, the treatment fluid devoid of thickener and colorant; and a fixer fluid including a precipitating agent, the fixer fluid devoid of colorant.
Furthermore, US 2014/0078217 provides a method of inkjet printing on non-porous media comprising inkjet printing a fixer fluid on the non-porous media and inkjet printing an ink onto the non-porous media, where the printing of the ink is within 125 milliseconds of the printing of the fixer fluid. Thus, the ink is printed to contact the fixer fluid within 125 milliseconds of each being printed.
The pre-treatment composition for inkjet printing disclosed in US 2012/0314000 comprises: a liquid vehicle, a fixing agent, a non-ionic defoaming surfactant, a surface tension reducing surfactant, and a latex resin having an acid number of less than 20.
Another example of a processing liquid for ink printing is described in U.S. Pat. No. 6,471,347. The processing liquid containing an insolubilizer of polymer as the insolubilizer disclosed therein is thinned out at a relatively low printing ratio, i.e., at a given ratio relative to dots of a black ink and applied after the Bk ink is applied. Thereby, a reacting product is fixed in a part relatively shallow and close to the surface of a printing medium without diffusing deep into the medium and thus can increase optical density of a printed phi image. In this case, the fixation can be accelerated when the processing liquid is highly penetrative.
However, primering behaviour results in unwanted side effects: the spreading rate of the ink is reduced. The effects of unstable jetting (jetting angle defects) become more visible (streakiness effect), and more ink volume is needed to cover the medium surface.
As a result, the addition of a second functionality in primer compositions to increase ink spreading would be favourable. This additive must be compatible with the primer salt composition itself, and preferably not compromise both jetting behaviour and drying behaviour of the primer layer.
Therefore there is a need for a primer composition which enables a better spreading of ink droplets.